1. Field
The present disclosure is directed to noise filters for serial data link receivers including all receivers for copper/optical/wireless links for local and remote data transmissions.
More particularly, this disclosure presents low cost high resolution noise filtering inverse transformation method, system and apparatus (NFIT) for precise recovery of originally transmitted signals from noisy received signals.
Solutions presented herein comprise systems and methods for programmable noise filtering from over-sampled wave-forms, carrying variable lengths data encoding pulses, which transfer data rates ranging up to ½ of technology's maximum clock frequency.
The NFIT shall be particularly advantageous in system on chip (SOC) implementations of signal processing systems.
2. Background
The purpose of noise filters is to reconstruct original signal by reduction of received signal components representing noise and/or by enhancement of received signal components representing the original signal.
Limitations of conventional noise filtering methods and electronic circuit technologies cause that only linear time invariant filters (LTI filters) can be used in majority of serial communication links.
Such LTI approximations impair filtering efficiency of the majority of the communication links which are non-linear and time variant and have changing in time characteristics.
Furthermore due to such limitations of conventional solutions; even rarely used non-linear and/or adaptive filters using adaptive algorithms to accommodate changing in time characteristics of transmission channels, can accommodate only limited and slowly changing portions of signal non-linearity and/or distortion caused by nonlinear and/or changing in time characteristics of transmission channel.
Frequency sampling filters (FSF) capable of recovering particular sinusoidal tones/sub-bands from a composite signal such as OFDM frame, were known and described as rarely used in the book by Richard G. Lyons; “Understanding Digital Signal Processing”, Second Edition 2004 Prentice Hall.
However such frequency sampling filters and other conventional frequency domain methods do not have time domain solutions needed to preserve and recover phase alignments of singular cycles of tones/sub-bands to the composite signal frame, wherein such phase alignments carry phases of tones/sub-bands transmitting data encoded originally.
It is the objective of solutions presented herein to alleviate such limitations by contributing;
accommodation of unlimited non-linearity and time variant quick changes of transmission channel such as those caused by line load, cross-talk and inter-band interference from adjacent transmission channels,
and said time domain solutions combining signal processing in frequency domain and time domain, in order to enable recovery of phases and amplitudes of singular cycles or half-cycles of data carrying tones or sub-bands comprised in the composite signal.